Vehicle heating and cooling systems provide pressurized hot and cold air flows that are ducted to varying points within the vehicle interior, for differing purposes. For example, hot and cold air both need to be delivered to vehicle passengers, but cold air does not have to be delivered to windows for defrosting purposes. If the same ducts were used to distribute both hot and cold air, then some cold air would be wasted out the window defrosting outlets. Since it is more expensive to provide cold air in a vehicle, this would be uneconomic. Therefore, it is generally desirable to provide separate ducts for hot and cold air. Typically, rigid wall ducts for hot and cold air are simply run side by side. This, of course, requires that each of the ducts be large enough in cross sectional area to handle the desired volume of air flow without restriction. In some cases, ducting has to be run through vehicle body locations where there is not sufficient space available to run two side by side ducts, each with the desired cross sectional area.